1. Field of the Invention
The present invention relates to a substrate identification circuit constructed from a thin film transistor formed on a substrate having an insulating surface, and a semiconductor device.
2. Description of the Related Art
In recent years, semiconductor devices, particularly electric equipment with semiconductor display portions have made remarkable developments. There are variety of application examples thereof, including game machines, notebook computers, portable equipment represented by mobile telephones, liquid crystal televisions, liquid crystal displays, electro-luminescent (EL) displays and the like. Compared to conventional cathode ray tubes (CRT), it is possible to form thinner lightweight displays for semiconductor display portions featuring low energy consumption.
Semiconductor display portions are classified into two types, a passive matrix type and an active matrix type, but in recent years especially, technologies for forming thin film transistors (TFTs) on a glass substrate have advanced, and applications and developments for active matrix type semiconductor device portions have progressed.
In particular, compared to a TFT with an amorphous silicon film, a TFT with a polycrystalline silicon film has a higher field effect mobility (also called mobility), and while conventionally the pixel is controlled by the driving circuit outside the substrate, it is now possible to control with the driving circuit formed on the same substrate on which the pixel is formed.
Also, if a TFT with a further higher field effect mobility is developed in the future, it is expected that a system-on-glass structure will be realized in which not only the driving circuit of the pixel portion but also various logic circuits such as operation processing and memories which are conventionally mounted outside the substrate as IC chips are formed on a glass substrate having pixel portions formed thereon.